Connectors that join optical fibers to create a low loss, separable optical interface have been available and in use for a number of years. These connectors use a variety of ferrule types, alignment schemes and latching mechanisms for joining solitary strands of single-mode and multi-mode optical fiber as well as a multiplicity of fibers in a ribbon form. An example of the second is typified by the xe2x80x9cMTxe2x80x9d style array ferrules. Each of these connectors join the fibers end to end using a variety of alignment techniques. For single fiber joints, an alignment ferrule generally surrounds and guides the fiber-ends together.
One application of optical connector technology is to provide an optical path for signals from board to board, or shelf to shelf within equipment chassis. This optical path is provided by passing optical fibers perpendicularly through a backplane, using so-called xe2x80x9cpass throughxe2x80x9doptical connectors. A right angle mounting of connectors join the optical fibers from an optical module on the daughtercard to optical fibers in cables running out of a card rack. This right angle mounting relies upon a blind mating of the fibers and must conform to standard cable management conventions such as minimum bend radius that contribute to box volume requirements behind the, backplane.
As the need for bandwidth capacity increases, xe2x80x9cOptical Backplanesxe2x80x9d usually in the form of laminated fiber matrices that overlay the backplane or that supplement the backplane are also being used. These optical backplanes, likewise have their fibers terminated to standard xe2x80x9cpass throughxe2x80x9d optical connectors as previously described.
With the recent advent of Vertical Cavity Surface Emitting Laser (VCSEL) transceiver arrays however, an opportunity exists to launch into fibers perpendicularly to or from the daughtercards or other printed circuit boards within the subrack. Typically, standard separable alignment techniques used for multi-fiber arrays, are used to connect the fibers to the VCSELs.
The current implementations of xe2x80x9coptical backplanexe2x80x9d or intra-box optical connections suffer from both reliability and performance limitations. Depending on the particular alignment mechanism used and the quality of the assembly, optical power losses can occur at the connection that degrade the signal.
Alignment tolerances required for optical connections are on the order of micrometers. These tight tolerance are difficult to achieve in a blind-mate connection. In addition, if multiple fibers are blind-mate aligned by pins or posts, the alignment tolerance due to stack up is not the same for all fiber pairs. This can induce uneven losses across the fibers and create skew among the signals in the fiber array. Moreover, if the daughtercard and backplane remain slightly out of perpendicularity after mating, the fiber surfaces will be further out of alignment with each other, inducing further losses.
In optical interconnect design, it is very important to have control and statistical knowledge of the losses in the optical path. This is because the design of the optical link tries to optimize the balance between providing enough optical power to achieve link performance goals, while trying to meet eye safety, thermal and cost goals.
Another limitation of current implementations results from the environment typically encountered by the optical connectors. These connections are typically within an equipment rack and are not easily cleaned. Dust and dirt are oftentimes carried by cooling fans or other motion within the equipment rack. As a result, mate and de-mate cycles of the connectors can then accumulate this debris on the mating surfaces, thus reducing the coupling efficiency of the optical connection. Some optical connector suppliers provide hinged shutters on portions of their connectors to minimize the contamination issues however, some dirt and dust can still get through during handling. In addition, shutters can also make the fibers more difficult to reach when cleaning is required.
Yet another limitation results from the nature of the xe2x80x9cpass throughxe2x80x9d optical interface onto the equipment backplane. A 90 degree turn by the optical fiber on the backplane is required. Current optical fiber technology requires the design to maintain a bend radius of greater than one inch to avoid optical loss and mechanical fatigue that can cause breakage. Fixtures that control the fiber bend radius are typically used. These fixtures gradually turn the fiber parallel to the backplane in order to plug to an overlay. Alternatively, fibers may be looped from one perpendicular xe2x80x9cpass throughxe2x80x9d to another to effect slot to slot connectivity. Both of these options, however, consume considerable space behind the traditional electrical backplane while radius fixtures add additional cost to the system.
In addition, using standard separable alignment techniques to connect fibers to VCSELs encounter the same sort of alignment and dust concerns previously stated. Moreover, these methods also consume a certain amount of length in the fiber that can be difficult to fit between card slots on a standard backplane.
One solution described in the following disclosure provides an electro-optical connector including a routing substrate with an optical transceiver mounted on the routing substrate. An optical fiber is connected to the optical transceiver and means are provided on the routing substrate to electrically connect to a circuit board. With such an arrangement, blind-mates at the optical connection are avoided while the tight alignment tolerances required by optical connections can be performed in a factory setting using precise alignment techniques thus minimizing optical losses due to misalignment of the fiber ends. As a result, losses in the optical path may be better controlled by a system designer.
Another solution described in the following disclosure provides an apparatus for transferring a signal between an optical fiber and a circuit board. The apparatus includes an electro-optical module with an optical connection between the optical fiber and the electro-optical module. The apparatus further includes a separable, electrical connection between the electro-optical module and the circuit board and driver electronics electrically connected to the electro-optical module. With such an arrangement, mate and de-mate cycles of the apparatus are performed at the separable, electrical connection rather than at the optical connection between the fiber and the electro-optical module. As a result, optical losses suffered at the connector due to contamination introduced during mate and de-mate cycles are eliminated as are future misalignments at the optical connection due to wear and tear on the alignment features. Moreover, strict cleaning procedures typically required at optical connections are avoided.
A third solution described in the following disclosure provides an electro-optical system including first and second circuit boards and first and second electro-optical modules. A first separable, electrical interface is provided between the first circuit board and the first electro-optical module and a second separable, electrical interface is provided between the second circuit board and the second electro-optical module. The system further includes first and second driver electronics electrically connected to a respective first or second electro-optical module and an optical fiber connected between the first and second electro-optical modules. With such an arrangement, bends in the optical fiber are no longer required thus eliminating the need for fixtures controlling the bend radius. In addition, space taken up behind the traditional electrical backplane by radius fixtures and looping of fibers is also eliminated.